The use of carbodiimides containing sterically hindered carbodiimide groups particularly as antiagers and, more particularly, as hydrolysis stabilizers for polyester polyurethanes is known. German Offenlegungsschrift 2,543,920. Such carbodiimides are generally obtained by condensation of monoisocyanates or of a mixture of mono- and polyisocyanates and are commercially available, for example, under the name Stabaxol (supplier Rheinchemie). Their hydrolysis-stabilizing effect is attributed to the reaction with free carboxyl groups (for example, from the adipic acid of the polyester) to acyl ureas. See, for example, W. Neumann and P. Fischer, Angewandte Chemie, 74 (1962), pages 801 et seq. Under certain conditions (for example, when polyurethanes stabilized with such carbodiimides are not properly processed), products that can adversely affect the health of the processor or user are released.
It is known that oligocarbodiimides and polycarbodiimides can be used as stabilizers, for example, for terephthalate fibers. In addition, carbodiimides and derivatives thereof, which may still contain, for example, free isocyanate groups, are known as modifiers for polyisocyanates and polyurethane foams. They are generally added to obtain certain physical properties, for example, a reduction in melting point. See, for example, German Auslegeschrift 2,837,770, U.S. Pat. No. 4,067,820, and German Offenlegungsschriften 2,714,292 and 2,714,293).
The object was to provide antiagers, in particular hydrolysis stabilizers, for plastics contain ester groups which, despite high activity, would not release volatile, possibly noxious, substances under conditions encountered during either processing or use.